The mission for emergency responders in northern Colorado Saturday: "To bring order to a chaotic situation," as an incident commander put it.

Waters receded some in the flood-devastated areas, but the rains were expected to fall heavy once again over the weekend.

At least four people have been killed and 172 are unaccounted for, officials say. The number of missing peaked at 218 and is expected to continue to shrink.

"We're assuming some of them have been stranded, we're assuming that some made their way out and simply haven't contact us or friends and family to get off the list, we're assuming that there may be further loss of life or injuries," Boulder County Sheriff Joe Pelle said.

"It's a sinking feeling," Pelle said, knowing that emergency responders may not be able to reach everyone who needs help.

The nightmare is far from over as the state awaits more rainfall, threatening to send swollen rivers gushing through streets choked with debris.

It will not be as much as the 15 inches dumped in some spots this week, but it could cause more flooding in areas where water has already receded, forecasters warned.